1. Field of the Invention
The present invention relates to a system and method for controlling a variable displacement engine.
2. Background Art
Fuel economy for a multi-cylinder internal combustion engine can be improved by deactivating some of the engine cylinders under certain operating conditions. Reducing the number of operating cylinders reduces the effective displacement of the engine such that it is sometimes referred to as a variable displacement engine. Depending upon the particular configuration of the variable displacement engine, one or more cylinders may be selectively deactivated to improve fuel economy under light load conditions, for example. In some engine configurations, a group of cylinders, which may be an entire bank of cylinders, is selectively deactivated.
Some variable displacement engines include separate intake manifolds and plenums for each bank of cylinders. When a bank of cylinders is deactivated, the intake manifold pressure approaches the current ambient barometric pressure. When reactivated, the bank of cylinders will produce near maximum torque until the associated manifold pressure is pulled down to a steady state vacuum.
The present invention pre-positions engine actuators based on engine operating conditions to reduce torque excursions during reactivation of a group or bank of cylinders.
Embodiments of the present invention include a system and method for controlling a variable displacement engine to deliver a desired torque that determine current engine operating conditions and pre-position one or more airflow actuators associated with one or more deactivated cylinders to provide the desired torque assuming those cylinders were activated. In one embodiment, the engine control strategy determines the cylinder air charge to achieve a desired torque based on engine speed, intake manifold pressure, and number of currently activated cylinders. A variable cam timing phase or angle associated with a deactivated cylinder bank is then pre-positioned based on the engine speed, intake manifold pressure, desired torque and number of cylinders to be reactivated.
The present invention provides a number of advantages. For example, the present invention uses pre-position control to reduce the time required to properly position airflow actuators when reactivating cylinders resulting in reduced torque variation or excursions from desired torque.
The above advantage and other advantages, objects, and features of the present invention will be readily apparent from the following detailed description of the preferred embodiments when taken in connection with the accompanying drawings.